The invention relates to a process for preparing alkoxymalononitriles.
International patent application WO-A-98/31652 describes the preparation of the anesthetic sevoflurane (fluoromethyl 1,1,1,3,3,3-hexafluoro-2-propyl ether) by reacting methoxymalononitrile with bromine trifluoride. However, WO-A-98/31652 does not disclose the preparation of methoxymalononitrile.
It is accordingly an object of the present invention to provide a process for preparing alkoxymalononitriles.
According to the invention, this object is achieved by the process according to claim 1.
It has been found that alkoxymalononitriles of the general formula 
where R1 is C1-6-alkyl or halogen-substituted C1-6-alkyl can be prepared by reacting the appropriate alkoxymalonamides of the general formula 
where R1 is as defined above with a dehydrating agent.
xe2x80x9cC1-6-alkylxe2x80x9d are here and hereinbelow all linear or branched alkyl groups having 1-6 carbon atoms, for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, tert-pentyl, neopentyl, hexyl or isohexyl.
xe2x80x9cHalogen-substituted C1-6-alkylxe2x80x9d are C1-6-alkyl groups which are mono- or polysubstituted by halogen. Preferred halogens are fluorine, chlorine and bromine. Particular preference is given to fluorine. Examples include: mono-, di- or trifluoromethyl, chloromethyl, bromomethyl, 1- or 2-fluoroethyl, 1- or 2-chloroethyl, 1- or 2-bromoethyl and 1-, 2- or 3-fluoropropyl.
The R1 radical is preferably methyl or trifluoromethyl.
Examples of useful dehydrating agents include trifluoroacetic anhydride, dibutyltin oxide, phosphorus oxychloride, phosphorus trichloride and phosphorus pentachloride. Preference is given to trifluoroacetic anhydride and phosphorus oxychloride.
The dehydrating agent is advantageously used in quantities of from 0.5 to 6 molar equivalent per amide group of the alkoxymalonamide of the formula II.
The dehydration is advantageously carried out in a suitable solvent. Examples of useful solvents include acetonitrile, dioxane, 1,2-dichloroethane, toluene, cyclohexane, heptane and octane. Preference is given to acetonitrile.
Preference is given to carrying out the dehydration in boiling solvent.
The dehydration is optionally carried out in the presence of a Lewis acid. Examples include the following Lewis acids: BF3, BCl3, BBr3, BI3, SbF5, AlCl3, AlBr3, TiBr4, TiCl4, TiCl3, ZrCl4, PF5, FeCl3 and FeBr3.
Preference is given to using AlCl3 as the Lewis acid. The quantity of Lewis acid is preferably from 0.01 to 0.05 molar equivalent.
The compounds of the formula II can be prepared by known processes. For example, Monatsh. Chem., 1965, 96, 1677-1689 describes a process for preparing alkoxymalonamides by reacting methyl alkoxyacetates with dialkyl oxalates and reacting the product (dialkyl alkoxymalonate) with liquid ammonia.
The dehydration according to the invention proceeds in two stages, and the intermediate product formed is the corresponding 2-cyano-2-alkoxyacetamide of the general formula 
where R1 is as defined above.
The 2-cyano-2-alkoxyacetamide (III) may be isolated or the dehydration reaction can be continued until the reaction product of the formula I is obtained.
To isolate the 2-cyano-2-alkoxyacetamide (III), the progress of the dehydration reaction is followed, for example by means of thin layer chromatography. The reaction is stopped at a suitable time, for example by cooling the boiling reaction mixture to 50-0xc2x0 C., preferably to about 0xc2x0 C.
The workup is effected by known methods, for example by means of extraction in the presence of a base and subsequent chromatography. An example of a useful base is sodium hydrogencarbonate.
The compounds of the formula III are chiral. They may be either in the S-configuration or the R-configuration. The above-described dehydration results in the racemate which may be separated into the two isomers by known processes, for example by HPLC chromatography using a column having a chiral stationary phase. Chiral stationary phases are known and commercially available, for example from E. Merck, Waters, Daicel or Macherey and Nagel.
The compounds of the formula III are novel and likewise form part of the subject-matter of the invention.
The compounds of the formula III can be converted in a similar manner to 2-cyanoacetamide, for example using 2-mercaptobenzoic acid to prepare 2-(4-oxobenzothiazin-2-yl)acetamide (N. S. Ibrahim et al., Heterocycles 1984, 22(8), 1677-1682), using 1,2-diaminobenzene to prepare benzimidazol-2-yl-acetonitrile (T. A. Fairley et al., J. Med. Chem. 1993, 36(12), 1746-1753) or using 2-cyanothioacetamide to prepare thiopyridines (R. M. Mohareb et al., Z. Naturforsch. B. Anorg. Chem. Org. Chem. 1986, 41(1), 105-109). Equally, the compounds of the formula III are useful for preparing barbiturates, coumarins or vitamins in a similar manner to the known use of 2-cyanoacetamide.
The examples hereinbelow illustrate the process according to the invention.